In known apparatuses of the above type, the cold air coming from outside the cabin of the vehicle, or perhaps from an air conditioning unit, is distributed between the cold air transmission branch and the air heating branch, which allows the temperature of the air which is received in the mixing zone, and which is then passed towards the outlet ports, that is to say the de-icing port, the aerators or cabin vents and the lower outlet ports which open into the lower part of the cabin, to be regulated.
The de-icing port, which is located close to the windshield, is adapted to be supplied essentially with warm air so as to cause the windshield to be freed of ice, or to be de-misted. The cabin vents or aerators, which are located at the level of the fascia panel, and thus at a lower level than the de-icing port, are arranged to be supplied preferentially with external cold air so that the occupants of the vehicle will receive cooler air around their faces. Finally, the ports situated in the lower part of the vehicle cabin, and therefore at a level lower than that of the aerators, are adapted to be supplied preferentially with warm air so as to provide heating around the feet of the occupants.
The distribution of the air flow between the various outlet vents or ports mentioned above is generally controlled by means of a first flap valve which controls the de-icing port and a second flap vale which controls at the same time both the aerators and the lower outlet ports.
In the known arrangements of the above type, the mixing zone is designed in such a way that the mixture of the cold air coming from the cold air transmission branch with warm air coming from the air heating branch is not complete, so that downstream of the mixing zone two air flows having different temperatures are obtained, these flows being led respectively to the various outlet ports. In this way a certain configuration of air distribution can be obtained which allows temperature to be stratified in the manner known as "bi-level". Under these conditions, the air stream at the higher temperature is led towards the ports located in the lower part of the vehicle cabin, while the air stream of lower temperature is led towards the upper part of the cabin, that is to say towards the de-icing port and/or the aerators.
Although this known solution achieves the objective of distributing cooler air through the aerators, it unfortunately also has the disadvantage of not facilitating de-icing or de-misting of the windshield, because the warm air which is delivered to the de-icing port is at a lower temperature than that which is led towards the feet of the occupants.
In the known arrangements, and for reasons connected with the mounting of the apparatus under the fascia panel of the vehicle, the cold air transmission branch extends generally horizontally, while the air heating branch is generally situated below the cold air transmission branch. Conventionally, the air heating branch is of a U-shaped configuration, with its outlet so directed as to deliver a flow of warm air upwardly.
It is thus desirable to be able to control the flow of cold air which is generally horizontal and the flow of warm air which is generally vertical, and which must be passed upwardly towards the de-icing port and/or be diverted downwardly towards the outlet ports in the lower part of the vehicle cabin, all to a greater or lesser degree according to the different distribution positions that may be selected.
Thus, in the position in which the aerators and the lower outlet ports are open at the same time (i.e. in the position known as the "aeration/foot" position), it is necessary to be able to deliver a stream of cold air towards the aerators and a stream of warm air towards the feet of the occupants, with a temperature difference of the order of 15 degrees C. between these two streams. By contrast, in the position in which the de-icing port and the lower outlet ports are open (which may be called "de-icing/foot" position), the warm air must be delivered at the same time and at the same temperature towards both the windscreen and the feet of the occupants.
The problem to be resolved is thus to control the flows of cold air and warm air coming respectively from the cold air transmission branch and from the air heating branch, in such a way as to allow the temperature difference between the two flows to be maximised in the aeration/foot position, but with no temperature difference in the de-icing/foot position.
In order to overcome this problem, it has already been proposed in Patent Specification No. 3 608 524 of the Federal Republic of Germany to provide a cold air duct extending directly from the cold air inlet to the aerators, which then allows a supplementary cold air stream to be delivered, if desired, to the aerators. Again, in the specification of French published patent application No. FR 2 562 845A, it has been proposed to provide, in the sides of the housing of the apparatus, and facing the outlet of the air heating branch, two deformations on the sides of the housing. This allows two quasi-ducts or flow paths to be created which direct warm air onto the sides, with the cold air passing directly through the middle and being controlled by a heater flap valve. This solution is not satisfactory, because it allows warm air to escape all the time through the two deformations mentioned above, so that a homogeneous mixture of the warm air with the cold air is not achieved.